Annealing effect on structural, morphological, and optical properties of reactive sputtered WO3 films for mediated heterogeneous photocatalyst

The reactive facing-target sputtering method was used to deposit WO3 thin films from a metal tungsten disk in an Ar+O2 mixture gas atmosphere at different sputtering pressures. X-ray diffraction, scanning electron microscopy (SEM), UV-visible spectrophotometer, and Raman studies were performed to study structural, surface morphology, and optical properties of the as-deposited and annealed samples. Annealing treatments were done in oxygen atmospheres. All the as-deposited films were amorphous in structure. The films annealed at 400 deg. C and deposited at 200 W show preferential orientation. SEM images show nanorodlike growth for the films deposited at a sputtering pressure of 0.15 Pa and annealed at 400 deg. C. The optical absorption edge of the as-deposited films prepared at the sputtering pressures of 0.8-0.15 Pa varied between 340 and 380 nm and shifted up to 480 nm when the samples were annealed at 400 deg. C. From Raman spectra, we observed the O-W6+-O bonds, and the W6+=O stretching mode of terminal atoms on the surface of WO3 microcrystalline grains. The crystal structures of the annealed films were of monoclinic phase. The suitability of the films for the WO3/TiO2 heterogeneous photocatalyst are analyzed and discussed